The invention relates to a process and apparatus for producing a twisted yarn from two slivers that are drawn to the desired size and are subsequently prestrengthened by means of pneumatic false twisting, the fiber ends being wound around the essentially unturned core, after which the prestrengthened slivers are twisted together with one another in such a way that the twisting turn is opposed to the winding-around direction, and to a feed spool for the twisting. The invention also relates to the twisted yarn feed spool formed by the process.
It is known (EP-A-38 143) to draw two slivers in a drafting frame to the desired size. Subsequently, these slivers, by means of pneumatic false twisting, are provided with a prestrengthening by means of which fiber ends are wound around the essentially unturned core of the slivers. The resulting prestrengthening of the slivers is so low that they cannot be used as individual threads or individual yarns. In the case of the known process, it is provided that the resistance to tearing of the finished twisted yarn is between 150% and 250% of the doubled, not yet twisted-together individual component. In the case of the known process, it is also provided that the twisting turn is opposed to the winding-around direction of the fiber ends so that during the twisting, the bundling is weakened that is obtained by the winding-around of the fiber ends. Since, however, in the case of the known process, the fiber ends are wound around in the form of spirals, i.e., essentially in a radial plane with respect to the core, this weakening of the bundling effect can hardly be achieved. In the case of the known process, it is therefore provided that wind-around fibers are wound around less than 50% and preferably less than 30% of the length of the slivers. This has the objective that subsequently, after the twisting, a yarn is created that is not very hard, like the known air yarns, but has an improved feel. However, in the case of this process, a relatively uneven twisted yarn is obtained that in the areas, in which the winding-around is present, has a hard feel but otherwise has a soft feel.
The invention is based on an objective of providing a process of the initially mentioned type in which a sufficiently firm, but at the same time voluminous yarn is obtained that has a high uniformity.
This objective is achieved by the fact that the fiber ends, in the form of helixes, are wound around the core with such a steep slope during the prestrengthening by pneumatic false twisting that, during the subsequent yarn twisting operation, the fiber ends that were previously wound around the core are as much as possible wound off the core.
By means of the helical winding-around during the prestrengthening, the advantageous effect is achieved that the slivers are prestrengthened over their length in a more uniform way. In addition, the special advantage is achieved that the areas that were surrounded by the winding during the prestrengthening, during the subsequent introduction of the twist, are loosened up again, because the winding-around is practically undone.
In a further development of the invention, it is provided that the predominant part of the fiber ends that were wound around the core of the sliver during the prestrengthening form helixes of an angle of slope of 45.degree. and more. This has the result that also these areas are reduced in which the winding-around sliver ends wind mutually around one another so that the opening-up of these windings is improved further during the twisting.
In a further development of the invention, it is provided that, during the prestrengthening, fiber ends are wound around the core of each of the slivers over the predominant part of the length and as uniformly as possible. As a result, the uniformity of the prestrengthened slivers and mainly the uniformity of the twisted yarn obtained later is improved significantly.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.